Field latex as the raw material of natural rubber contains protein and the like contaminants which vary in their qualities and quantities depending on the terrain, season, climate and the like of the place of production, and these contaminants cause problems such as the onset of an allergic reaction on human by the resulting rubber products and variation in the quality of the products. Because of this, the field latex is deproteinized by its treatment with water and a surfactant or with a proteolytic enzyme.
In the treatment with a proteolytic enzyme, protein molecules on the surface of natural rubber latex and in serum are hydrolyzed by the enzyme. The treatment can remove the protein highly accurately as compared with the simple treatment with water and an surfactant, hence providing a natural rubber latex product which contains substantially no protein.
As an known example of the aforementioned deproteinized natural rubber latex, natural rubber latex is purified by treating it with a proteolytic enzyme, diluting the treated latex with water and/or a surfactant and then subjecting the diluted preparation to centrifugation to separate and remove the protein.
However, the deproteinized natural rubber latex produced in this manner has drawbacks in that the product has a poor film-forming property and the resulting raw rubber film shows a poor green strength, causing generation of cracks and the like. In addition, the production process itself also has a disadvantage from a production efficiency point of view, because recovery yield of the natural rubber latex is poor due to a large number of latex particles inevitably remained in the protein-containing phase at the time of centrifugation and great labor is required to remove aggregated latex particles generated inside the centrifuge.